The applicants have demonstrated that acute stress can result in measurable myocardial damage. Technetium-99m-bone-seeking agents were used to quantitate the extent of the stress-induced myocardial damage (SIMD). With this quantitation, a series of experiments are proposed involving the following: First, a systematic study of the subject's (Sprague-Dawley rat) interaction with a stressful environment to determine those factors which are contributing to the myocardial damage. These experiments include an examination of subjective vs. objective stress; the effect of early coping experience on subsequent stress; and the effect of variations in the state of arousal on SIMD. Second, an investigation of several procedures to reduce the SIMD, including trained relaxation and aerobic exercise. Third, an examination of the possibility that the previously observed SIMD may be due to increased platelet aggregation. Radioactively labeled platelets, developed by the applicants, will be injected with and without anti-platelet drugs and the platelet accumulation in coronary vessels will be compared to the measured SIMD.